Method and related tools for cold forming of inside threads and grooves



Dec. 29, 1970 cs. ABUHAB 3,550,174

METHOD AND RELATED TOOLS FOR COLD FORMING 0F INSIDE THREADS AND GROOVESFiled April 14. 1967 2 Sheets-Sheet 1 qmmu unp "e: m i

INVENTOR Abuhab ATT OILNL. 3

Dec. 29, 1970 G. ABUHAB 3,550,114

\ I METHOD AND RELAT TOO FOR COLD FORMING 0F INSIDE ND GROOVES T EADFiled April 14, 1967 2 Sheets-Sheet 2 T l I: 9 T a} a mvsmoa 2L 17 2 BYAbuhab ATTOILNEBS United States Patent US. Cl. 152 2 Claims ABSTRACT OFTHE DISCLOSURE Entire internal threads and grooves are simultaneouslycold formed in workpieces by the use of an expansible cylindrical sleeveor segment chasers. A supporting shaft is provided with conical portionsadapted to receive the sleeve or the segment chasers and to guide theirthreadforming portions into a workpiece.

The purpose of the present invention is a new method to obtain internalthreads and grooves by cold forming.

A further object of this invention are the devices or tools used torealize this method, essentially constituted of threading elements inthe shape of a one-piece sleeve, or individual chaser combsalternatively and guided by conical supports.

The conventional method to obtain internal threads or grooves is the useof cutting tools, known by the name of taps. The inconveniencespresented through the use of such tools are among others, the rapid lossof cutting edge, the difiiculty of correct resharpening and the frequenoccurrence of enlarged threads, notably at the beginning of the threads.Furthermore, the lubricating and cooling oil can be hardly reusedbecause of its mixing with the chips resulting from the cuttingoperation.

Another known process is of cold forming. To accomplish it, the toolsusually employed are subject to a lot of disadvantages.

In effect, the tools used in the process above referred are the socalled solid cold forming taps of polygonal section, with a conicalpoint that enters the hole to be threaded, the diameter of which isaprpoximately equal to the pitch diameter of the desired threads. Thetools are forced through the extension of the hole the thread resultingformed, under cold conditions.

The solid taps do not permit recuperation, it being frequently seen thatthey are worn out not uniformly over their length; also it frequentlybecomes difficult to obtain uniform threads at the entrance of theinternal threads.

Further, it is suitable to cite that all type of tools until now knownare of a high cost of production because of their special polygonalconfiguration associated with reduced durability and high cost of thesteel they must be made of.

Besides, these taps only permit obtaining standardized threads, and inthe eventual need for internal threads of over-standard or sub-standarddimensions, the manufacture of special taps at a greatly increased priceor cost is required.

Still another disadvantage of these taps resides in the difiiculty toobtain the desired concentricity and parallelism between the geometricaxis of the hole and the axis of the thread made in it.

A further disadvantage peculiar to the taps until now employed is thenecessity of these to be Withdrawn from the hole by rotation thereofthat is to say they must be unscrewed after forming the screw thread.

The main object of the present invention is to provide a method ofobtaining internal threads or grooves of whatever diameter andlongitudinal dimension by means of Patented Dec. 29, 1970 cold forming(without cutting) obtaining a thread uniformity, and coincidence of thecenter line of the hole with the center line of the thread.

Another object of this invention is the provision of two basic types oftools, needed to accomplish the cold forming process. These tools areessentially constituted by a conical guiding pin which supports thethreaded forming element (which, as stated before, can be an expandablesleeve or a set of chasers). This thread forming element moves axiallyalongside the guiding pin under the effect of a force applied parallelto the axis of the pin. Thus, it causes the expanding of the threadingelement and the subsequent deformation of the internal walls of the holein which it was introduced, cold forming the thread.

It is obvious that the problems of the lack of parallelism andconcentricity presented through tools used to date can be avoided. Theemployment of this new method and related devices is speciallyrecommendable for mass production.

A simple mechanism may be used to support the tool and to give it theproper movement of oscillation. Then a source of power-mechanical,hydraulic or pneumaticis applied to the threading device with forcenecessary to expand the device to the predetermined diameter for thecold forming of internal threads or grooves.

A fixture will hold the work-part in alignment with the tool, notpermitting angular movement.

It follows that the purpose of this invention is to present a method,and the means to realize it: to tap by cold forming method internalthreads and grooves of whatever type, dimension and diameter desiredsuch as buttress thread, standard threads and others without limitationof diameter size or longitudinal dimension, including left hand threadsand taper threads.

This operation is economically and technically more advantageous becausethe internal threads thus obtained comply with minimum tolerances andhave a better finish.

Still another purpose is to supply threading devices of tools of greaterdurability, since these tools, have no cutting edges.

Another object of this invention is to provide internal threads withover-standard and under-standard diameters, thus reducing quantativelythe number of necessary tools to cover the most varied range of internalthread diameters.

Another advantage lies in the fact that while the cutting of thematerial is eliminated, there are no chips produced during the coldforming process, preventing the tool to get stuck and permitting totalreuse of the lubricatingcooling oil without previous filtering.

Still another advantage is represented by the accelera tion of theoperation of internal threading, since the unscrewing of the formingtool is not required, it being suflicient to ease the force applied tothe threading element to permit its contraction and consequent axialwithdrawal from the threaded hole, without the threads being touched bythe forming tools. This characteristic is one of the most important,qualifying the tool of this invention for top productions.

A final advantage lies in the economic aspect of the invention,considering the high level production and the possibility of reusing thetools by successive reconstitution of the cold forming elements, givinglonger durability and lower manufacturing cost.

It is possible to produce internal threads by this method of coldforming in most ferrous metals-including stainless steel-as well as inmany of the non-ferrous metals such as brass, copper, aluminum andothers.

The invention will be better visualized in the light of the attacheddrawings showing two alternative embodiments of the tools to realize themethod of this invention.

FIG. 1 is a broken elevation of a device to accomplish the method ofthis invention.

FIG. 2 is a lateral View of the same device mounted in its non-operativecondition.

FIG. 3 is a lateral view of FIG. 2 showing the tool in workingconditions.

FIG. 4 is a broken view of an alternative embodiment of the device toaccomplish the process of this invention.

FIG. 5 is a cross section view through lines IVIV of FIG. 4.

FIG. 6 is a lateral view of FIG. 4 in non-operative conditions, but atthe beginning of the operation.

FIG. 7 is the same view of FIG. 6 with the threading element in finalworking conditions.

From the attached drawings it is verified that the device for tapping orcold forming of internal threads, object of the present invention, isessentially composed of two concentric elements (FIG. 1) one being acore, constituted by an axle 1 with an extremity conically shaped 2 overwhich slides axially cylindrical sleeve 3, having internal passage forthe conical end of axle 1.

Said sleeve or bushing is externally provided with an intermediatethreaded area 5 interrupted by longitudinal slots 6 that, in number, areproportional to the dimensions of the bushing, itself.

The bushing is driven while sliding over the conical extremity 2, bymeans of radial pins 7 projecting through the slots 6.

To start the threading operation the expandable bushing 3 is assembledto the shaft 1, being freely introduced into the orifice 8 of theworkpiece 9 (FIG. 2). The external diameter of the threaded sector 5 issmaller upon entry than the pitch diameter of the thread to be obtainedin the hole of the workpiece 9 while the diameter of the hole 3 is aboutthe same as the pitch diameter of the thread to be cold formed.

Once the device is inserted into the workpiece 9 an oscillating movementis given to the drive shaft with amplitude of about 90. The samemovement is transmitted to the bushing 3 solidarized to the shaft 1through the pins 7 inserted into the slots 6, of the said bushing 3.

At the same time when the alternating angular rotation is beingexecuted,'a force F is applied to the sleeve 3 in the longitudinaldirection parallel to the geometric axis of the assembly. This causesthe sliding of the bushing 3 alongside the drive shaft 1 originating theprogressive expansion of the bushing 3 and consequently, the greaterpenetration of the forming threads 5 into the internal surface 8 of thehole, displacing the material under cold condition thus forming, thedesired internal thread.

When the above operation is over, it is enough to ease the pressureexercised through the force F by which the threads 5 of the bushing aredisengaged from the internal threads permitting removal of the bushing,now contracted to its original dimensions, from the workpiece 9, whilethe drive shaft 1 is still in movement.

The described operation should be executed preferably by means of asimple mechanism that permits holding the workpiece 9 as securelydesirable, while it does not allow angular movement, and also permitsthe oscillating movement of the tool with contemporaneous application ofthe force F by the pneumatic or hydraulic mechanism means.

In the remaining figures (4 to 7), an alternative embodiment of the toolis illustrated for cold forming of inside threads or grooves inaccordance with this invention, conserving basically the conception ofan expansion threading element that slides axially alongside thefrustoconical extremity of a supporting shaft.

FIG. 4 shows the axle 11 whose free extremity is provided with acylindrical enlargement 12 (FIG. 5) longi- 4 tudinally cut with channels13 0f which the bottom surfaces 14 are inclined forming in the whole aninternal tapering stem shape (FIGS. 4 and 5).

In the same channels, chaser combs 15 are assembled with a slidingadjustment, having as many chasers as the number of channels. Theassembly is made in a predetermined sequence.

The chasers have a working surface constituted of thread segments whichcorrespond to the internal thread or groove desired. The segments ofthread have a rather thin edge to permit an easier penetration in theworkpiece. Each chaser has, following the work zone, a depression 17ending with an enlargement 18 (FIG. 4). All chasers are guided by thebottom 14 of the channels 13.

Once the oscillating movement R of the arbor 11 is started, with amaximum amplitude of 90, the force F is also applied in the longitudinaldirection parallel to the axle (FIG. 7) by means of an outer flange 21and inner flange 21a, thus assuring a uniform distribution of pressureon all the chasers 15 and of its regular advance through the guidechannelsv 13 pressing with progressive intensity the material of theworkpiece 20 until the desired internal thread is completed under coldconditions.

Once the operation is finished, it is suflicient to ease the pressureresulting from the application of force F permitting the free withdrawalof the tool by means of the sliding of the chaser combs alongside therespective channels and consequent retraction of these chasers withouttouching the newly formed screw threads.

It is obvious that the length of the total threaded part 5 of thebushings 3 and 16 of the chasers is dimensioned in such a way that itwould always be bigger that the longitudinal dimension of the threads tobe made, which in the majority of the case is less than 1% times thediameter of the hole.

It is obvious that the invention has been merely exemplified in theattached drawings as disclosed hereinbefore, which do not constitute alimitation to its scope it being well possible, for instance, to providea further embodiment of the tool to be used in a rotary movement,instead of alternate angular rotary movement, it being enough to makesuitable beveled arrangement of the first threads of the tool.

I claim:

1. A method of swaging internal threads within an opening provided in aworkpiece comprising the steps of placing an expandible swaging tooltherewithin and then subjecting said tool to simultaneous rotary andexpansion movement so that radial and torque forces are applied on theentire forming surface of said opening until said threads are fullyformed.

2. A method as described in claim 1 including initially placing saidtool within said opening in a retracted position, applying, gradually,an axial force during said rotary movement until the tool is fullyexpanded so as to form the entire surface to be threaded in oneoperation, and thence releasing the axial force so as to retract saidtool, and thence withdrawing said tool from said opening.

References Cited UNITED STATES PATENTS 2,616,103 11/1952 Stecher l011,782,804 11/1930 Breitenstein 10145 1,905,709 4/1933 Herman 10-1452,556,174 6/1951 Evans 10152. 2,712,658 7/ 1955 Strickland l01452,828,493 4/1958 Koehler 10152 CHARLES W. LANHAM, Primary Examiner E. M.COMBS, Assistant Examiner

